- Clinical science
Vaccination is a very effective measure for providing immunity to many infectious diseases. The discovery of vaccines played a central part in the eradication of smallpox and helped significantly reduce the incidence of potentially severe diseases such as poliomyelitis and measles. Live vaccines (attenuated, i.e. non-infective pathogens) or inactivated vaccines (subunits or complete pathogens) are used to achieve active immunization, which enables the host's immune system to build up a sustained immune response to specific pathogens. The immune response may be measured and quantified by assessing the antibody titer. In the event of potential disease (e.g., after exposure to high-risk pathogens), if the immune system is unable to produce sufficient antibodies fast enough, passive immunization can offer immediate short-term protection via direct injection of pooled antibodies for many conditions. Modern vaccines are usually well tolerated, and adverse events are rare. However, the intervals between vaccine administration and possible contraindications must be considered.
For CDC vaccination recommendations, see article on .
- A product (e.g., dead or weakened organism) that provides immunity from a disease
- May be administered through injection, orally, or nasally
- Vaccination: administration of a vaccine that induces immunity against an organism
- The process by which a person becomes protected from a disease
- Vaccines and recovering from some infections cause immunization
- Mechanism of action
- Application: Vaccines are available for intramuscular as well as for intravenous injection.
- Simultaneous vaccination: ≥ 1 vaccine administered on the same day, but in different syringes and at different anatomical locations
- After administration of a passive vaccine against a specific pathogen, a live vaccine against the same pathogen should not be administered for at least 3 months.
- General information
Current vaccination recommendations for the US can be found in the.
- Definition: Modified functioning virus or bacterium. The vaccine has the ability to replicate in the patient's body but does not cause disease.
- Mechanism of action
- Oral vaccine or subcutaneous/intramuscular injection in children > 12 months
- Not indicated in children < 9 months; (the rotavirus vaccine is an exception, which is first given at 6 weeks of age)
- Usually lifelong immunization
- Second dose usually recommended to “catch” non-responders (not as a boost)
- Multiple live vaccines can be given simultaneously, but if given at different times they should be at least 4 weeks apart to avoid possible interference.
- May be administered simultaneously with inactivated vaccines
- Available vaccines
- Special considerations: Live attenuated vaccines can theoretically revert back to their disease-causing form. However, this has only been observed in the case of the oral polio vaccine.
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Common adverse effects 
- Affects ∼ 1/3
- Usually begin within the first 48–72 hours after administration and last 1–2 days
- Live attenuated vaccine: can cause mild form of the disease, usually appearing within 1–3 weeks of administration; : usually caused by replication of the attenuated vaccine strain
Rare adverse effects
- Serious allergic reaction (generally < 1 per million doses)
- Live attenuated vaccine: attenuated course of the disease following immunization (e.g., vaccine-related measles)
- Vaccine injury (∼ 1/1,000,000): permanent injury from a vaccination or a vaccine-related complication (e.g., encephalopathy, seizures, brachial neuritis)
There is no link between autism and vaccines or their ingredients. 
- Severe, acute illness: e.g., infection with fever > 38.5°C (> 101.3°F)
- Previous adverse reaction related to a vaccination: e.g. anaphylaxis
- Severe allergies to components of a vaccine: e.g., egg white in some live vaccines (e.g., yellow fever)
Live vaccinations are not recommended for
- Pregnant individuals
- Immunodeficient individuals
- Rotavirus vaccine: severe combined immunodeficiency (SCID), history of intussusception; , uncorrected GI tract malformation (e.g., Meckel's diverticulum)
- Hepatitis B: infant weighing less than 2 kg
- Tetanus: Guillain-Barré syndrome within 6 weeks after a previous dose of tetanus toxoid-containing vaccine
- Pertussis-containing vaccines; : known anaphylactic reactions, encephalopathy within 7 days following previous vaccination, progressive or unstable neurologic disorder (e.g., coma, uncontrolled seizures, or progressive encephalopathy)